the opposite of serious could be playful,joyful or happy :)
The opposite is unserious.
There is no opposite word for felony. You may be thinkning of the lesser offense, known as a misdemeanor. Both are offenses, but one is more serious than the other.
Silly or goofy
The opposite would be the rarely-used form "tragical" or more commonly "tragic." Other antonyms would be serious, unfunny, sad, or unfortunate.
Serious, earnest.
to joke to joke to joke
Frivolous
Sin importancia.
Competent serious.,
The word duchess does not have an opposite. There are some serious misunderstandings about the meaning of the word opposite. A duke is a counterpart of duchess; it is not opposite.
Are you serious? A positive number.